Power distribution centers (PDCs) are commonly used in automotive vehicles to simplify electrical system wiring by eliminating multi-branch wiring and consolidating fuses, relays, and other electrical components in a single location. A PDC is often mounted within the vehicle's engine compartment and typically comprises a junction block having a plurality of receptacles disposed on a mounting surface for receiving electrical connectors, fuses, relays, and other components. Electrical terminals are retained within chambers internal to the junction block beneath the receptacles such that the electrical components make contact with the terminals when they are inserted into their respective receptacles. The PDC often has one or more removable housings to protect the junction block, the electrical components and the terminals from contaminants such as dirt, water, salt and other debris that may be present in the vehicle engine compartment.
Typically, assembly of the PDC involves inserting the electrical terminals into the chambers from the underside of the junction block. It is necessary that the terminals be securely retained in the chambers so that they are not pushed downward when the electrical components are inserted into the receptacles, as this will prevent proper contact between the components and the terminals.
U.S. Pat. No. 5,257,951 discloses apparatus for securing electrical terminals within a junction block. As seen in FIGS. 5 and 6, the junction block 100 has a series of receptacles 102 disposed in a straight line on an upper surface and chambers 104 defined by chamber walls 106 molded integrally with the junction block below the surface. Three parallel passages 108 extend into the junction block 100 and communicate with each of the chambers 104 in the line. A terminal holder 110 comprises three arms 112 extending in parallel from an end plate 114. After the terminals 116 have been inserted into their respective chambers 104, the holder arms 112 are inserted into the passages 108. As seen in FIG. 6, the two lower arms pass beneath shoulders of the terminals to prevent downward movement, and the third arm passes between adjacent terminals to urge flexible walls 118 separating the terminals from one another toward positions tending to hold the terminals in place. The terminal holder disclosed in the '951 patent has been found to provide inadequate protection against entry of contaminants into the passages into which the holder arms are inserted. Since the passages offer direct access to the terminal chambers, any penetration by contaminants could cause corrosion of the terminals and have a detrimental effect upon the electrical connections within the junction block.
FIGS. 7 and 8 depict a prior art PDC which provides; improved protection against entry of contaminants into the passages. The PDC comprises a junction block 120, a terminal holder 122, and top and bottom housings 124,126 for the junction block. A row of receptacles 128 is formed in the upper surface of the junction block for receiving electrical components (not shown) such as fuses or relays. Chambers 130 for housing electrical terminals 132 are formed integrally with the block directly below and in communication with the receptacles 128.
The junction block has a side wall 134 extending downwardly from the upper surface, and a rectangular gap 136 is formed in the side wall adjacent the end of the row of receptacles such that the openings of the passages 121 are recessed inwardly from the surface of the side wall. The terminal holder 122 is substantially identical to the holder 114 described hereinabove with reference to the '951 patent, and when the arms 138 thereof are inserted fully into the passages 121, the end plate 140 fits into the gap 136 such that the outermost surface of the end plate is recessed inwardly from the outer surface of the junction block side wall 134, as best seen in the cross-sectional view of FIG. 8.
Lower housing 126 has a first tab 142 extending upwardly from an upper edge thereof at a position which coincides with the gap 136 in the junction block side wall 134. Upper housing 124 has an outwardly flared skirt 154 forming its lower edge, and a second tab 156 projects downwardly from the skirt at a position which coincides with the gap in the junction block side wall.
After the terminal holder 122 has been inserted fully into the junction block 120, the lower housing 126 is mated with the junction block to cover the lower surface thereof. The upper edge of the housing fits inside of the junction block side wall and the lower tab passes upwardly on the inside of the side wall 134 to cover the lower portion of the terminal holder end plate 140, trapping the holder in the fully inserted position, as seen in FIG. 8. The lower housing 126 is maintained in connection with the junction block 120 by mating latch members on the two pieces, as is well known in the art. The upper housing 124 is then mated with the junction block 120 such that the skirt 154 fits downwardly over and surrounds the top edge of the side wall 134, the second tab 156 fitting into the upper portion of the gap 136 and overlapping the lower tab 142 by a small distance. Accordingly, the two tabs 142,156 cover the terminal holder end plate 140 and so provide improved protection against the intrusion of contaminants into the passages.
The presence of the tabs on the upper and lower housings,, however, has been found to make it more difficult to property assemble the housings with the junction block. Specifically, in some PDCs the upper housing is attached to the junction block by first engaging one edge of the housing with the junction block and then tipping or rotating the housing downwardly toward the upper surface of the block in a hinging-type movement about that edge until the entire housing is properly positioned and secured to the block. If, as may often be the case, the tab on the upper housing is located on an edge which is perpendicular to the hinge edge, the tab does not follow a straight path as it fits into the gap but rather travels in an arcuate path during the hinging movement. Accordingly, the lower corners of the tab will strike the side wall rather than fitting smoothly into the gap, interfering with closing of the housing.
Further, the tabs are quite thin and flexible and so are subject to being inadvertently bent to configurations that may prevent them from fitting properly into their respective gaps. If the tabs are not positioned properly with respect to the gap when mating of the housings is attempted, they may bend or break when the housings are assembled with the junction block, thereby providing inadequate protection against contamination. Bending of the tabs may also prevent proper assembly of the housings with the junction block.